Malondialdehyde (MDA) is found in modest amounts in meat and some other foods. Preliminary studies have implicated it as a mutagen and carcinogen. Studies will be conducted to determine its carcinogenicity when it is chronically administered orally or intrarectally in Sprague-Dawley rats for one year. In separate studies, rats will be maintained on diets of either rat chow, hamburger, wheat, rat chow plus 20% safflower oil, or rat chow plus 20% lard for two weeks and then sacrificed. The gastrointestinal contents will be assayed for MDA. Correlations between the dose response data from the carcinogenicity studies and the MDA content of the gastrointestinal tract will be attempted to give some estimate of the potential risk of dietary MDA carcinogenicity.